MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - help on 2 areas - fuel pump set up and rear wheel

Hi

looking for a bit of help / advice

firstly setting up the fuel system on my resto

as far as i can see there is the pipe from the fuel tank to the pump then from the pump to the fuel line / carbs - plus the wiring one earthed to the bracket and one positive from the loom - where do the 2 breather pipes from the boot go too ? i can't work that out - will probe be simple ? any advice / photos ?


also the rear axle bolt that locks on the hub - i know that one is a right and one if a left handed thread - firstly do these need to be torqued up and 2ndly anyone know what size spanner or socket fits these?

thanks in advance
richard weaver

The breathers will depend on whether you have an original AUF214 pump or not.

If you do, there should be a stub from the side of the body and another from the plastic cap.

As for the rear hub nuts, yes, the RH is righthanded and the LH is lefthanded.

The subject of torque figures has cropped up many times. Some people have quoted a figure, others have said there isn't one. Some say don't do them very tight, as it is only a thin nut, others (me included) say do them as tight as you can with a 2-foot bar.

I've never stripped one, but I've seen them come loose from not being tightened enough.
Dave O'Neill 2

x2 what Dave said

The nut is 1.5" diameter, 12 threads / inch and 1/4" thick. Calculating the max torque on that nut using the Machinery's Handbook formula comes up with a number over 900 ft-lbs, so there should be no problem with applying 140 ~ 150 ft-lbs to the nut (this is the torque value given in the A30 shop manual, which our rear axle was borrowed from).

The socket is a 1 7/8", and because the nut is thin it is a good idea to grind the end of the socket down so that the radius is eliminated as much as possible, so you get the maximum amount of engagement to avoid it slipping and rounding the nut.

Here is a link to a great website with more details on the nut torque,
http://mgaguru.com/mgtech/rearaxle/ra102.htm



Norm
Norm Kerr

Yes, not nice if they come undone, this is what happens ...


Paul Walbran

If you haven't got the correct socket, use stilsons.

As for how tight. 140lbft is disputed and very likely to strip the nut or threads on the axle. Just do it very tight, and bend the lock tab over.

I've NEVER had one come lose by doing them up as I show in my picture. I doubt I get much more than 50lbft.

Btw, the pic (RHS) shows it being undone. The other side is an LH thread.




Lawrence Slater

The theory is that driving with the nut loose for a long time may allow the nut to move around, and erode the threads on the axle housing, leading to weak threads which could strip when torqued. Healthy axle housings have no trouble at all with the torque of 150+ ft lbs.

Actually, an old BMC mechanic who chimed in on this issue here before said they never used a torque wrench, they had a really long breaker bar and they would STAND on it (probably resulting in torque far above 300ft lbs, if the bar was 2 ft long and their mechanics weighed 150lbs who were standing on it).

The risk of a too loose nut is possible wheel loss.
The risk of a too tight nut is possible strip, but only if the housing was damaged already (actually not causing a problem, but revealing an underlying problem).

If you use a plumbers wrench (monkey wrench) the nut gets chewed up, but the nuts are pretty cheap to replace if they get unsightly.



Norm
Norm Kerr

If you have some scrap metal handy, you could knock up a spanner. I used some 2mm sheet strengthened with weld and an old tommy-bar and put a longish pipe wrench over it. It was a lot cheaper than a correct spanner and did the job.


Nick Nakorn

Neat.

I need to make something for my MGB, which has an octagonal nut, annoyingly!
Dave O'Neill 2

Norm, can you post a pic of the text from the A30 w/shop manual, where it states that the torque on the rear hub nut is 140lbft?

"The theory is that driving with the nut loose for a long time may allow the nut to move around === "

Obviously if left loose, it will cause problems. Nobody suggests leaving the nuts loose. The front hub nuts are tightened to circa 50lbft, and they don't come loose. So why would the rear hub nuts come lose?. Vibration? If so, then why don't the front hub nuts come loose? The fronts have split pins, and the rears have lock tabs, just like crankshaft main caps.

And as I've said before, the wrench doesn't chew the nut, and the nuts on my hubs are the originals.

I like that spanner though Nick, I think I might make one myself.

Lawrence Slater

Here's a picture of the official BMC service tool used to remove and tighten the rear hub nut.

How do you get a torque wrench on that? That's why the BMC mechanics didn't torque it I'd imagine.




Lawrence Slater

I have one of these tools. The tommy bar is 12" long 1/2" dia. I have always done it up 'tight' as per the workshop manual and given the leverage its probably well over 100lbft.
Bob Beaumont

I used to concur with Lawrence on this one, believing that the nut was really there to resist lateral forces trying to pull the wheel off when cornering. So it needed to be tight for safety, but not massively tight.

But the article that Norm links to, although relating to an MGA axle does raise other explanations as to why they should be done up very tight. It also explains how what appears to me to be quite a fine and delicate thread will in fact take a very much higher torque without stripping. Unless of course it has already been damaged over the years by being insufficiently tight.

The existence of the "Workshop Tool" of course doesn't prove anything regarding how tight they were done at the factory. Factory methods of assembly were notoriously "unique" with whatever was devised as easiest or most effective for workers on the assembly line. So doors were adjusted for fit by jamming a bit of wood in the door opening and kicking or leaning on the door top until it twisted to the right shape. And I have no doubt that if the rear wheel nut was to be done up "F*%ki*g" tight (technical term) then the easiest way would be to throw the "workshop tool" in the skip and use a big box spanner and a long scaffold pipe.
Guy Weller

Hi Lawrence,

I wish I had a copy of that A30 manual page, someone else posted reference to it here one time when this conversation was covered a few years ago (probably the thread where I was convinced about the importance of the torque!, because I, too, used to think it didn't matter, and that the tab washer would control it enough, until the old mechanics convinced me otherwise), but they never did share a scan of the page, just verbal.

Someone else chimed in with the torque from an MGB, and then there's the link to the MGA website which talks about it in detail, and since all of those axles are substantially similar to ours (if there is a difference in nut size, or in thread size, it must only be an increment of difference due to size, rather than a drastic design difference), it implies that their information is applicable for us too.

BMC had a habit of not repeating their instruction in the shop manuals (which is why the Bentley manual had to include all those pages from the 948 and 1098 engined versions of the car in their 1275 edition "General Information" section, to cover the suspension springs and other things that hadn't changed over the years). I have assumed they just forgot to include that rear nut instruction while doing so!

Norm
Norm Kerr

Hi Norm.
Well I can't comment on why the MGA/MGB or other cars that share the SAME SIZE axles need 180lbft, because I've never owned one. But since I've had my Sprite for over 36 years, and have NEVER tightened the rear hub nut to anything near 70lbft, let alone 140lbft, I reckon I can safely say that not doing so, doesn't result in the bearing rocking on the axle and or ruining it or damaging the thread. I think I'd have noticed by now.

So why hasn't my rear hub nut come loose and caused the damaged described in that MGA guru link?

I managed to download a PDF copy of the A35 workshop manual by Cassell and Company. No mention of the hub nut torque. However it does contradict the the MGA guru statement that the bearing is a location fit. Cassell says it's a press fit on the axle. The LEYLAND manual says the bearing is a press fit in the hub, and is drifted onto the axle. Clearly there is NOT meant to be a working clearance.

So has anyone got access to a BMC A30/A35 workshop manual?

As for BMC not quoting a torque in the official Spridget manual; Since these cars were in production for a long time, I reckon that over that time, if the nuts were not being done up tight enough, then the torque spec would eventually have been mentioned as being important. And yet, it's not in ANY publication that I'm aware of.

Unitl it was mentioned here on this BB, I have NEVER heard of ANYONE doing the rear hub nut that tight on a Spridget.

So based on my experience I haven't changed my mind at all. As long as you do it "tight" which to me will be similar to the front hubs, you won't get a problem.

Regarding the tool. If it was neccessary to torque it, I'm pretty certain that BMC ewould have said so. On page 302 they show a 140lbft torque wrench. Part number 18G372. Why list that for other uses, and not mention that the rear hub nut should be torqued to 140?

I don't buy it. You don't need to do the rear hub to 140lbft.

If of course you have a damaged hub or axle, because perhaps previously someone left the nut really loose, then you probably can overcome that by tightening the nut really tight. But how tight?

Can someone with a 140lbft plus torque wrench and the appropriate size socket, please see how tight you can get that nut before you strip the thread?

It will be an interesting experiment if nothing else.

Of course it would need to be a spare axle, just in case you ruin the thread.





Lawrence Slater

The reference to being 'absolutely tight' is made by Mike Garton in his book 'Tuning BMC Sports Cars' published in 1970. Mike is a very well known Sprite racer having owned ex works Sprites and winning a number of racing awards in the 60's. He ended up as technical correspondent at BL's special tuning department. He states 'the nut must be really tight to stop the bearing turning on the axle casing and in the hub. Any play can result in the hub failing'. There is no mention of a torque setting. The special tool illustrated is made for both Spridgets and MGA/B. One end for the 6 sided Spridget nut and the other for the 8 sided MGB one. The tube on the end of the tool slips inside the axle casing and stops the tool slipping off when a high tightening force is applied.
Bob Beaumont

"absolutely tight."

Sure. But define that. No one doubts that the nut should be tight enough. But what denotes tight enough? And tightening the nut doesn't influence the fit in the hub, which is a press fit -- or in my case hammered in, and secured additionally by the half shaft flange/brake drum/road wheel.

Maybe this comes from the racing fraternity, where the extra stress caused by racing 'has' caused axles/hubs to fail unless the nut is done to a greater tightness than usual for the road car. But again, if so, it's even more surprising that given the influence of the racing connection, BMC/BL didn't quote a torque figure.

Telling people to do it 'tight' is open to interpretation. Quoting a torque spec, isn't.

The head, crank caps, front hubs, diff nut, etc, -- all are quoted. If it was vital, so would the rear hub nut have been I reckon.
Lawrence Slater

If the torque wrench shown is 140 lbs/ft and there is no torque figure quoted for the rear hub nut, maybe 'tight' is more than 140.

I may be able to get sight of a BMC A30 manual in the next week or so.

I have a spare axle I could experiment on, but if it hasn't stripped before I reach the limit of my torque wrench, I won't know at which point it does strip.

There is also the issue of how to hold the spare axle whilst trying to tighten the nut. I really struggled to dismantle an A30 axle 'off the car', as I couldn't easily hold the axle while trying to turn the hub nuts. Judging by the folds of the tab washers, they had never been undone before, and they were VERY tight.
Dave O'Neill 2

I agree Lawrence. If it was that critical then there would be a figure quoted. As I have said looking at the tool it would be capable of easily capable of getting over 100ft lb.
Bob Beaumont

I don't think the torque is critical and tend to agree with Lawrence and Bob. The nut is in any case tabbed and the bearing is a very close fit. Assuming the bearing has lubrication there's no problem with bearings becoming loose.
Nick Nakorn

The way I interpret it, is that if it was critical the MINIMUM tightness would be quoted. They wouldn't have just said tight ot very tight, as that is open to misinterpretation.

They(BMC and other publications) bother to mention other safety issues, and yet fail to mention that if the rear hub nut isn't 140lbft, your wheel can fall off? Nah. I don't accept it.

I also don't buy this 'explanation' that the wheel bearing can move back and forth on the axle shaft as the car moves off and stops, and thus cause the nut to rotate undone. If that were possible, why doesn't it happen to the front hubs too?

If it's possible for the inner race to rotate on the axle shaft if the nut isn't tight enough, then I would imagine that the pretty experienced bods at BMC would have noticed that.

I note that some here have changed their minds as a result of reading that it should be circa 140lbft, and yet until they read that, they had been doing their nuts up to an amount that is probably way below that, as have I. None of those have reported a problem hitherto, and I haven't either.

Even if it is proveds that the nut/axle thread is capable of taking 140lbft, or 900 as Norm says. That's still no reason to go that far. The reason the nut is that size, is that the half shaft has to pass through the center of it. Contrast with the hubs on the front, where the axles are solid, not hollow.

Interestingly, every link I've searched to find where the 140lbft figure comes from, seems to lead back to Norm. He quotes what the nut is capable of, and concludes therefore that's what it should be.

You won't convince me, because it's not neccessary. I WILL however be convinced, if I read an authoritative BMC/BL text that says it is.
Lawrence Slater

I wish that all shop manuals were perfectly written, so that we could use them as the last word, bible of truth, but mistakes and omissions in them do happen, as we well know.
When the manual fails to explain something, the logical course of action is to see what standard industry practice would be (and bolt thread calculations are very well established, and easy to look up in any number of engineering texts, Machinery's Handbook, etc). Alternatively, look up on other manuals with similar structures (like the MGA and the MGB), for guidance.

So, when I was confronted with this question, and read the old mechanics who said they'd never measured it but always used a bloody long breaker bar and set it "really tight", I wondered why it was OK for it to be so vague (once again, a 2 ft breaker bar with a 150lb guy standing on it = 300 ft lbs, as a point of reference).

All I did, then, was calculate using industry standards to find what it was capable of (900ftlbs), and you are right Lawrence, it is so much only because it had to be so large to let the axle through. Realizing this helped me to understand why the final torque used on it had so much allowable range.

Unfortunately, this does not answer the question of "what is the minimum?"


Perhaps the minimum is "greater than 0"? I mean, there is a tab washer that is supposed to hold it from rotating, and, I agree with you, Lawrence, there might not be much actual rotational load on the nut. It would depend entirely on the drag in the hub bearing, and it would tend to only occur in a loosening direction when driving in reverse.


In any case, a fastener should be tightened some minimal % of its ultimate torque in order to stretch it enough for clamping action to occur (that is what threaded fasteners are, "rubber bands" that hold things together so they don't move under load).

So, as with all things not expressly defined in the shop manual, going back to industry standard practice, which states something in the order of 10 or 20% minimum (actually, there are formulas but they depend on knowing what the loading is in the joint and that would take a detailed knowledge of the axle design that isn't available 50 years after it was designed but could probably be figured out if it was important enough).

Bringing us back to, "probably the torque on that nut ought to be in the 90 ~ 180 ft lbs range", the point of concern would be making sure it was tight enough to prevent the bearing from moving around and wearing out the axle housing.

The other useful reference is the people who have reported the removal effort required on those nuts when taken off of axles that show signs of having never been apart since leaving the factory. They also said it was tight enough to require a long breaker bar.


Another way to look at how to answer this question is this: If one would like to experiment with their own car and see how low they could go with the torque, and then after 100,000 miles of use report their finding, that would still only say what works for one single assembly. If one would like to responsibly advise others in what they should do with their (random quality) cars, it is preferable, usually, to advise them based on what all of the evidence points us to, which is in the neighborhood of 100 or 150 ft lbs.


Norm
Norm Kerr

"The other useful reference is the people who have reported the removal effort required on those nuts when taken off of axles that show signs of having never been apart since leaving the factory. They also said it was tight enough to require a long breaker bar."

One word Norm. Stiction. This was discussed last year if you recall.

And as for showing signs of never been off, just the other day I had the LH rear hub off my midget. The lock tab looked truly perfect, exactly as if it had never been disturbed. Guess what bearing it had in it? 6207. A modern replacement. The RH side also had a perfect lock tab, but it still has an RHP in it. So clearly it's not always so obvious, and i didn't need a long bar to undo the nuts. Just my stilsons with no extension.

"If one would like to experiment with their own car and see how low they could go with the torque, and then after 100,000 miles --- "

Well as it happens, I can report that after 100K miles, and having only ever used stilsons to tighten my nuts, without standing on the stilsons, my nuts haven't come loose, my hubs still require that the bearing be hammered in, and the axle still needs the bearing to be pressed or hammered on.

My guidance is to copy how it feels to do up the front hub nuts, but without using a torque wrench, since I don't have a 1.7/8" socket. If it's good enough for the front hubs, why isn't it good enough for the rear hubs?

Having said all that, if someone proves that the spridget axle/nut can handle 140 plus of torque, then why not whack 'em up that tight.

I'm simply saying that it isn't neccessary, and until not so long ago on here, most people agreed. What's changed? After 50/60 years, have people suddenly started to report hub failure or wheels falling off? Not as far as I know.

I think you are a worrier Norm. Maybe it's a creeping US thing. All worried about being sued for killing someone, if you don't cover every angle. So belt, braces, reinforced eyelets in yer trousers, and make sure to disconnect the battery when changing a side light bulb. :).
Lawrence Slater

Having tightened the nuts on the rear axle to 140 lb/ft, I can confirm the axle takes it no problem.

The only problem was keeping the socket on the nut.

dominic clancy

Here's a snip from the BMC MGB workshop manual.


Dave O'Neill 2

For all the argument and difference of opinion, I rather suspect that in practice there isn't that much difference. It is really very easy even without resorting to long breaker bars, or jumping up and down on long levers, to exert over 100ft lbs The fact that the nut is large and needs either a large socket or a fairly beefy stillson or similar to grip it would also tend towards tightening with a fair amount of effort. I therefore suspect that those (like Lawrence) who follow the "do it up very tight" policy are probably exerting 100 + ft lbs at the least. 100 really isn't that much.
Guy Weller

Nick,
I'm intrigued to know how you cut the hexagon shape?
M J Chapman

"100 really isn't that much"

When I assisted graeme last year with his diff nut, once we got to 100 it took 2 of us to hold the diff down. So I think 100 without a decent length of lever is a fair bit of effort. I hardly exert myself when doing my hub nuts up, and I only weigh a little over 10.5stn.
Lawrence Slater

MJ, I drilled a few holes and used a jigsaw to join them up and then tidied it up with a dremel and hand files.


Nick Nakorn

Just how I imagined you did it.

Think I'll make mine next week, but I'm going to make it into a socket by welding a bit of steel tube to it, and then the lot to an old redundant 1/2" drive socket so I can get my torque wrench on it for my max reading of 100lbft. Just so I can conform to the worry camp. LOL. ;)

Cheaper than buying one, but a lot more time and effort. Jeez I'm a tight bastard. lol.
Lawrence Slater

Rather than a socket, you could weld a nut onto it.
Dave O'Neill 2

A good idea Dave.

I'll have to check, but I think my old nuts are big enough. lol.
Lawrence Slater

You could weld in a centre bar that goes inside tthe axle tube to give extra stability - as with the workshop tool
Guy Weller

I had thought of using a piece of an old halfshaft, so it would have the bar for stability, welding pieces of steel onto the inside of the flange in order to grip the nut, then weld a large nut onto the outside to turn it.

Unfortunately, old MGB halfhafts seem to be few and far between.

I already have a socket for Spridgets.
Dave O'Neill 2

Hi

Is the socket size for the Spridget rear hub nut 1 5/8 inch, not 1 7/8 inch?

Thanks
Mike
M Wood

Just watched the St Mary's Trophy race from Goodwood.

A Riley 1.5 lost its rear wheel, complete with hub and halfshaft.

I don't know how tight the hub nut was, but it obviously wasn't tight enough!


Dave O'Neill 2

I always wanted one of those Rileys. I reckon if I'd bought one, I'd still have it today.

And I'd still be doing my nuts up with stilsons :).
Lawrence Slater

Hi Mike,

the socket is 1 7/8" (I just went and double checked for you to be sure!)

:)



Norm

Norm Kerr

I knocked up my rear hub nut removal tool today. Took about an hour. Looks very crude I have to admit, but it's also very effective, and that's what counts.

6mm plate and a 3/4 af bolt head.

I've had the LH rear hub and back plate off my Sprite. So I used it first to tighten the hub without a torque wrench. I just used an extended T bar, which is little longer than the length of my Stilsons handle. Did the nut up to what I reckon is tight enough, -- and felt the same as using my stilsons, and then a little bit more. I wouldn't have wanted to go more than that I reckoned.

Then I put the torque wrench on it set at 55lbft. Click.
60lbft, click.
65lbft, click.
70lbft, moved a tad, and click.

Ok, I admit, using my stilsons I might possibly have been achieving more than the 50lbft I reckoned earlier. But not much, if at all.

The new tool with a socket, is much easier to use, and I had a longer lever. Using my stilsons I was nowhere near getting to 70lbft, let alone 100lbft.

It feels bloody tight at 70lbft, and I'm completely confident that it won't come undone.


Lawrence Slater

Hi Norm

Many thanks for popping out to measure the socket size - what a gent!

Lawrence, Nick and others - you seen the hub nut spanner available from an Australian specialist?
http://spriteparts.com.au/shop/accessories.html#RearHubNutSpanner (from a useful USA thread: http://www.mgexp.com/phorum/read.php?3,1957453)

Cheers
Mike
M Wood

Very nice Mick. But I don't see that it's any better than the tool I've just knocked up. Mine fits properly and doesn't slip off, even without being bolted to the hub. It's also compact and fits more easily in the tool box.

All that's wrong with mine is how it looks -- if that's important that is. If it is, then make one like Nick's, which looks very nice. :).

And the beauty of home made, is that it's better for the environment, in that it uses up scrap metal. ;). It's also VERY cheap.

I commend it to the board. lol.
Lawrence Slater

Lawrence

Yes, your homemade one looks good. It was interesting how someone else had come up with the same solution.

Cheers
Mike



M Wood

Nick gave me the idea lower down.

Previously my Stilsons did the job, but I have to say my home made tool is easier.
Lawrence Slater

This thread was discussed between 09/09/2014 and 28/09/2014

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.